This application for a Mentored Research Scientist Development Award (K01) seeks support for development of a unique program of interdisciplinary independent research that combines social theories and research methods of social organization with that of infectious disease dynamics to study ways in which the social organization of communities may simultaneously impact access to social resources and transmission of infectious diseases including HIV. The K01 will support structured training, coursework, tutorials, intensive mentored relationships, and empirical research within a rigorous interdisciplinary institutional environment. Specific training objectives are to obtain: 1) expertie in sociometric network concepts, methods, and measures; 2) skills in phylogenetic analysis and infectious disease dynamics theories; and 3) expertise in the study of social organization and social capital; and to: 4) integrate new skills and concepts with current research to inform intervention development and seek funding as an independent scientist. The proposed training and research is a natural next career step that builds upon a background of social, behavioral, and epidemiological HIV and substance use research and is responsive to identified priorities for U.S. HIV prevention. The disproportionate and severe HIV epidemic among African-American men who have sex with men (AAMSM) requires an understanding of community social dynamics in order to advance development of interventions that integrate behavioral, structural, and biomedical components. A long-term goal is to understand how the social organization of AAMSM communities, their socio-economic stability, and their HIV transmission dynamics are interrelated to inform innovative HIV prevention and care interventions. The objective of this research is to examine HIV transmission pathways and access to social capital within AAMSM social and affiliation networks and establish a methodological, theoretical, and operational foundation for future research. Research specific aims are to: 1) evaluate HIV phylogenetic clustering and identify characteristics of persons in clusters with AAMSM; 2) determine presence and correlates of network social capital among AAMSM; and 3) characterize AAMSM affiliations with formal organizations and social settings and identify affiliation network influences on HIV and substance use. These hypotheses will be tested through examination of HIV genetic sequence data collected among approximately 2000 HIV-positive individuals in Maryland between 2012-2015, including an anticipated 38% AAMSM, and primary data collection with 300 adult AAMSM in Baltimore, Maryland. Findings will inform the approach and conceptual framework and provide skills for a broader R01 study examining pathways between social structures and HIV transmission. The research and training from the award will result in scientific publications that will provide insight into social and structural influences on HIV transmission among AAMSM and provide direction for intervention development.